In order to provide an electrical isolation between two electronic components or parts, for example between a substrate and a semiconductor die which is mounted onto the substrate or a semiconductor die mounted on another semiconductor die, the electrical isolation should show a low tendency for electro-chemical migration effects and for partial discharge effects.
Electro-chemical migration (ECM) in general is the migration of metal ions through a polymer matrix or along an interface of a polymer matrix. ECM is typically accelerated by electrical fields and humidity. Furthermore, ECM might be accompanied by chemical effects within the polymer matrix. Certain traces of materials, such as e.g. Cl or S, in the polymer matrix accelerate the effect. ECM eventually might even lead to a formation of short circuits between high and low voltage electronic components. Typical substances being prone to ECM effects are conductive glues, i.e. polymers filled with metallic particles (typically Ag, Au, Ni, Sn, Pt, Pd or alloys thereof). The materials not only migrate through the polymer matrix of the glue but also through adjacent materials, e.g. mold compounds or other encapsulation materials. ECM-induced growth of conductive paths may lead to a degradation in the isolation properties (break-through-voltage) and therefore to a reduction in the lifetime of an electronic product.
Partial Discharge (PD) in general is the local re-arrangement of electrical charges in the vicinity of inhomogeneities, for example in voids. Such an effect may lead to a partial degradation of a corresponding material and may reduce break-through isolation properties and thus, the lifetime of a product.
In order to avoid ECM and/or PD, a non-conductive glue may be used, wherein such a glue may have limited isolation properties what may lead to a low break-through-voltage and partial discharge. Alternatively, a glued isolation platelet including for example glass, oxidized silicon, ceramic and/or an organic material may be used between the two electronic components. However, this platelet again may be glued either using non-conductive glue what may lead to the above PD problems or using a conductive glue, wherein the platelet itself may be configured to provide sufficient isolation, what may solve the PD-challenge, but may be prone to the above described ECM problems.